1. Field of the Invention
The present invention relates to a scanner in which a light beam is deflected to scan a scanning surface, and more specifically to a scanner which is provided with a device for adjusting an incident position of a light beam on a photo-detector used for determining the timing of commencement of writing each scanning line with respect to a scanning surface.
2. Description of the Related Art
A laser-beam printer provided with a laser-beam scanner is well known. In a laser-beam printer, a laser beam which is modulated in accordance with image signals to be output from a laser-beam emitter is deflected by a polygon mirror to scan a photoconductive surface of a photoconductive drum in the main scanning direction to thereby form a main scanning line in the photoconductive surface. The laser emission is turned ON and OFF in accordance with given image signals to draw a corresponding image (charge-latent image) on the photoconductive surface of the drum, and subsequently this image drawn on the photoconductive surface of the drum is transferred to plain paper according to a conventional electrophotographic method. Dry powder (e.g., toner) that adheres only to the charged area is applied to the drum, transferred to the plain paper and fused by heat. Such a laser-beam printer is widely used; e.g., as an output device for a computer.
In a laser-beam scanner provided in such a laser-beam printer, a photo-detector (i.e., a laser-beam detector) is generally fixed at a position outside the latent-image-forming scanning range to detect the scanning laser beam before it starts generating each scanning line. The photo-detector generates a pulse signal each time the scanning laser beam is incident on the photo-detector. The pulse signals output from the photo-detector are input to a processor, and subsequently the processor generates corresponding horizontal synchronizing pulses (HSYNC) to determine the timing of commencement of writing main scanning data, namely, writing each main scanning line.
In such a laser-beam scanner, two types of devices for adjusting the timing of commencement of writing each main scanning line with respect to the photoconductive surface of the drum (i.e., for adjusting the timing of generating horizontal synchronizing pulses) are known. In each type of adjusting device, a reflecting mirror is arranged at a position outside the latent-image-forming-scanning range to detect the scanning laser beam before it starts generating each scanning line, while a photo-detector is arranged at a position on the path of the laser beam reflected by the reflecting mirror. In one type of adjusting device, the reflecting mirror is rotatable so that the incident position of the laser beam on the photo-detector can be adjusted, which makes it possible to adjust the timing of generating horizontal synchronizing pulses. In the other type of adjusting device, the reflecting mirror is fixed while the photo-detector is linearly movable so that the incident position of the laser beam on the photo-detector can be adjusted.
In the former type of adjusting device, although the incident position of the laser beam on the photo-detector can be adjusted by rotating the reflecting mirror, it is difficult to finely adjust the incident position of the laser beam on the photo-detector. Furthermore, the reflective mirror needs to be accurately and precisely positioned on a base on which the reflective mirror is to be mounted. In the latter type of adjusting device, the position at which the photo-detector is to be arranged is quite limited. Moreover, in each type of adjusting device, in the case where the base on which the reflective mirror and the photo-detector are mounted is slightly deformed after a long period of use, the respective positions of the reflective mirror and the photo-detector deviate from their original positions. In this case, the respective positions of the reflective mirror and the photo-detector cannot be easily adjusted from outside the laser-beam apparatus.
An object of the present invention is to provide a scanner provided with a device for adjusting the incident position of a light beam on a photo-detector used for determining the timing of commencement of writing each scanning line with respect to a scanning surface, wherein the adjusting device makes it possible to finely and easily adjust the incident position of the light beam on the photo-detector.
Another object of the present invention is to provide a scanner having such an adjusting device which makes it possible to finely and easily adjust the incident position even from outside the scanner.
Other aspects, objects and advantages of the present invention will become apparent to one skilled in the art from the following disclosure and the appended claims.
According to an aspect of the present invention, there is provided a scanner including a light-beam emitter for emitting a light beam; a light-beam deflector for deflecting the light beam to scan a scanning surface; a photo-detector provided at a position outside an image-forming scanning range of the scanning surface to detect a scanning light beam before the scanning light beam starts generating a scanning line in the image-forming scanning range; a rotatable member, located in front of an incident surface of the photo-detector, that is rotatable about a rotational axis perpendicular to a plane defined by the scanning light beam by the deflector; an optical member, provided on the rotatable member, that allows the scanning light beam to pass therethrough to be incident upon the incident surface of the photo-detector; and a device for adjusting rotational position of the rotatable member about the rotational axis.
Preferably, the light-beam deflector includes a polygon mirror.
Preferably, a signal, output from the photo-detector, is used for detecting the timing for commencement of writing the scanning line with respect to the scanning surface.
The optical member can include a cylindrical lens or a plane-parallel plate. Preferably, the optical member includes a member having an optical axis which lies in a plane defined by the scanning light beam, and the rotational axis extends perpendicular to the optical axis.
The rotatable member can be positioned in a recess formed in a housing to be rotatable about the rotational axis.
In an embodiment, the recess is a circular recess, and the rotatable member includes a disc portion which is fitted into the circular recess to be rotatable about the rotational axis.
Alternatively, the rotatable member includes a shaft coaxial to the rotational axis, and the rotatable member is positioned in the recess with the shaft being inserted into a hole formed at the bottom of the recess so that the rotatable member is rotatable about the shaft.
Further, the recess can be formed on an outer surface of the housing, and a through hole through which the optical member is inserted in the housing is formed at the bottom of said recess, and the rotatable member is positioned in the recess with the optical member being inserted into the housing through the through hole.
For holding the rotatable member at an adjusted position, the adjusting device can include at least one set screw which penetrates into the rotatable member through a slot formed thereon to be screwed into the housing.
Alternatively, it is possible that the adjusting device includes a member, fixed to the housing, for pressing the rotatable member against the bottom of the recess. Preferably, the pressing member includes a spring. Further, the spring can be a leaf spring fixed to the housing by at least one set screw.
Preferably, the scanner further includes a device for rotating the rotatable member about the rotational axis.
In an embodiment, the rotating device includes a radial slot formed on the rotatable member to extend in a radial direction thereof; and a rotating tool engageable with the rotatable member to rotate the rotatable member about the rotational axis. Namely, the tool includes an engaging pin engageable with the radial slot, an axis of the engaging pin deviating from a rotational axis of the rotating tool.
Alternatively, the rotating device includes a circumferential gear formed on an outer peripheral surface of the rotatable member; and a rotating tool engageable with the rotatable member to rotate the rotatable member about the rotational axis. Namely, the rotating tool includes a pinon gear which is engaged with the circumferential gear.
It is preferable that the scanning surface is a photoconductive surface of a photoconductive drum.
In an embodiment, the photo-detector and the light-beam emitter are supported on a common circuit substrate and do not relatively move.
The scanner can include an fxcex8 reflecting lens that reflects the scanning light beam deflected by the light-beam deflector to the scanning surface.
According to another aspect of the present invention, there is provided a scanner including a light-beam emitter for emitting a light beam; a light-beam deflector for deflecting the light beam to scan a scanning surface; a photo-detector provided at a position outside an image-forming scanning range of the scanning surface to detect a scanning light beam before the scanning light beam starts generating a scanning line, the photo-detector generating an output signal upon detecting the scanning light beam to determine a timing of commencement of writing the scanning line with respect to the scanning surface; and an optical member for deflecting the scanning light beam to be incident on the photo-detector in a direction to vary the timing of the scanning light beam incident upon the photo-detector.
The present disclosure relates to subject matter contained in Japanese Patent Application No. 10-92725 (filed on Mar. 19, 1998) which is expressly incorporated herein by reference in its entirety.